Timing-based servo (“TBS”) is a technology developed for linear tape drives. In TBS systems, recorded servo patterns consist of transitions with two different azimuthal slopes. Lateral read/write head position is derived from the relative timing of detected pulses, or dibits, sensed by a plurality of servo sensors disposed on the read/write head. TBS patterns also allow the encoding of additional longitudinal position (“LPOS”) information without affecting the generation of the transversal position error signals (“PES”). This is obtained by shifting transitions from their nominal pattern position using pulse-position modulation (“PPM”). A specification for the servo format in current midrange tape drives is provided by the linear tape-open (“LTO”) format. The complete format for LTO drives of generation 1 (LTO-1) was standardized by the European Computer Manufacturers Association (“ECMA”) in 2001 as ECMA-319.
In tape drives, two dedicated servo channels are normally available from which LPOS information and PES can be derived. A signal from one servo channel may occasionally fade while the other signal from the other servo channel might not be detected. In such an event, the servo channel affected by fading loses timing and needs to undergo re-acquisition. Consequently, additional latency and loss of information is experienced.